The present invention relates to the field of additives for fluids such as automatic transmission fluids, traction fluids, fluids for continuously variable transmission fluids (CVTs), dual clutch automatic transmission fluids, farm tractor fluids, and engine lubricants.
In the automatic transmission marketplace, where there is rapid engineering change driven by the desire to reduce weight and increase transmission capacity, there is a desire for automatic transmission fluids that exhibit a high static coefficient of friction for improved clutch holding capacity. At the same time, there is a desire to improve the retention of positive slope characteristics in the μ/v (coefficient of friction vs. sliding speed) curve. There are newer tests in the marketplace which are used to define these characteristics. The static torque can be measured in tests such as the Toyota SAE#2 friction test procedure and the retention of positive slope can be measured by procedures like the JASO LVFA (Japan Automotive Standards Organization, Low Velocity Friction Apparatus) in which the slope of the μ/v curve is periodically measured during oxidative and mechanical aging.
There are patents, for example, U.S. Pat. No. 5,750,476, where a type of friction modifier technology used to achieve this performance is described. The combined requirements of high static coefficient of friction and durable positive slope are often incompatible with traditional ATF friction modifier technology which is extremely well described in the patent literature. Many of the commonly used friction modifiers result in a low static coefficient of friction and are not durable enough on positive slope to be of sufficient use. Additional patent literature describing technology for retaining positive mu/v or anti-shudder characteristics include U.S. Pat. No. 5,858,929. These may employ metal detergents and combinations of friction modifiers.
U.S. Pat. No. 4,512,903, Schlicht et al., Apr. 23, 1985, discloses amides prepared from mono- or poly hydroxy-substituted aliphatic monocarboxylic acids and primary or secondary amines, useful as friction reducing agents.
PCT Publication WO04/007652, Adams et al, Jan. 22, 2004, discloses a fluid composition of (a) a friction modifier derived from the reaction of a carboxylic acid with an amino alcohol, the friction modifier containing at least two hydrocarbyl groups, and (b) a dispersant, which provides good friction properties in an automatic transmission.
U.S. Pat. No. 4,886,612 discloses a lubricating oil comprising at least one of various products, which can be various imidazolines or an oxazoline of the structure
where R2 and R3 each represent CH2OCOR1, CH2OH or H, prepared by the condensation a carboxylic acid (or a reactive equivalent thereof) with an amino alcohol; for example, the condensation of two moles of isostearic acid with one mole of tris-hydroxymethylaminomethane (THAM).
The present invention solves the problem of developing new and relatively simple and inexpensive friction modifiers to obtain high static coefficients of friction and maintain a durable positive slope during oxidative and mechanical stressing of the friction system for use in a mechanical device such as an automatic transmission. Moreover, the formulations of the present invention exhibit good anti-shudder durability and friction stability in automatic transmission testing, in combination with good oxidative stability and low copper corrosion. This is accomplished at least in part by the use of a friction modifier which comprises the condensation product of a secondary amine having two alkyl groups of at least 6 carbon atoms, with a hydroxyacid or hydroxythioacid, in combination with other components, as further described in detail below. The compositions are useful, among other applications, for lubricating a transmission such as an automatic transmission, including different varieties of transmissions such as traction drives, continuously variable transmissions, dual clutch transmissions, and hybrid manual-automatic transmissions, as well as transmissions for hybrid gasoline/electric vehicles.